1. Field of the Invention
This invention relates to a magnetic sensor for detecting a magnetic signal from a magnetic recording medium utilizing variation in the resistance value of a magneto-resistance effect element.
2. Description of the Related Art
In order to detect a magnetic signal from a magnetic recording medium, there has been utilized a magnetic sensor in which the magnetic signal is converted to an electrical signal by a magneto-resistance effect element and then the electrical signal is subjected to processing. This type of magnetic sensor has been disclosed in Japanese Unexamined Published (Laid-open) Patent Application No. Sho-54-41335. In this magnetic sensor, a pair of comb-shaped patterns are disposed so as to be perpendicular to a plane containing a magnetized pattern on a magnetic recording medium (hereinafter referred to as "magnetized pattern plane) which has been periodically magnetized at a pitch .lambda. of magnetic poles (hereinafter referred to as "magnetizing pitch") in such a manner as to be positionally deviated by .lambda./2 on a plane in parallel with the direction of the magnetized pattern. However, in the manner as described above, when the magnetized pattern is so designed as to have an extremely minute magnetizing pitch .lambda. in order to improve resolution, the intensity of a rotating magnetic field within a plane containing the comb-shaped patterns is weakened and thus the magneto-resistance effect element can not be magnetized to saturation. Therefore, this magnetic sensor has the shortcoming that a satisfactory detection can not be performed.
In order to overcome the above shortcoming, there has been further proposed a magnetic sensor in which two magneto-resistance effect elements are disposed in parallel to the magnetized pattern plane, but perpendicular to the magnetizing direction of the magnetized pattern, as disclosed in Japanese Examined Published Patent Application No. Hei-2-16973. In this case, in the same manner as shown in FIG. 6, N and S magnetic poles are alternately disposed on the magnetic recording medium at an interval of .lambda., and two striped magneto-resistance effect strip-shaped elements are disposed spacedly from each other at an interval of .lambda./2. The two magneto-resistance effect elements are connected to each other in series, and both ends of the serially-connected elements are provided with a power source terminal. An output of these magneto-resistance effect elements is obtained at an output terminal which is provided to a conjunctive point of the elements. When a current flows through the magneto-resistance effect elements while a magnetic field is applied to the elements in a direction perpendicular to a direction of the current, a resistance value between both terminals of the elements varies as shown in FIG. 5. As is apparent from FIG. 5, if an area which is not magnetically saturated (hereinafter referred to as "non-saturation area") is utilized in the resistance-variation rate as shown in FIG. 5, a substantially sinusoidal output can be obtained. This magnetic sensor utilizes the above characteristic. That is, since the intensity of a magnetic field which is applied to the magneto-resistance effect elements varies in a sinusoidal form by rotating the magnetic recording medium or the like, the output waveform of the resistance-variation which is obtained at the output terminal is also substantially sinusoidal. The thus obtained sinusoidal output is subjected to waveform processing to be converted to a rectangular waveform, whereby variation of the magnetic signal is detected.
This magnetic sensor is required to actuate the magneto-resistance effect element while the output of the element is not saturated and to output a sinusoidal-waveform signal at the output terminal. Therefore, the gap between the magnetic recording medium and the magnetic sensor is set to be relatively large, and thus the intensity of the magnetic field which is applied to the magnetic sensor is weakened. However, there are some cases where the gap between the magnetic recording medium and the magnetic sensor must be set to a short distance. In these cases, the intensity of the magnetic field which is applied to the magnetic sensor is unintentionally excessively strengthened, so that the magneto-resistance effect element is saturated and the output waveform thereof is extremely distorted. Therefore, in the waveform shaping operation of the sinusoidal waveform to the rectangular waveform, the gradient of the output sinusoidal voltage is moderated in the vicinity of a comparing level as indicated by a dotted circle of FIG. 7. For example, the output signal of rectangular waveform greatly varies merely when the comparing level is slightly fluctuated (within plus or minus 8 mV) due to the temperature drift of a processing circuit or the like, and thus it is difficult to detect a magnetized position.
The distance of the gap between the magnetic recording medium and the magnetic sensor is mainly dependent on design accuracy of the magnetic recording medium, but is also dependent on unavoidable factors such as eccentricity of the axis of the magnetic recording medium and so on. Therefore, there has been required a magnetic sensor for obtaining an output signal having a large or sharp gradient in the vicinity of the comparing level.
In order to satisfy the above requirement, a magnetic sensor as disclosed in Japanese Unexamined Published Patent Application No. Sho-63-302319 has been proposed. This magnetic sensor comprises two pairs of patterns confronting a magnetic recording medium having a magnetizing pitch of .lambda., one of which patterns includes two magneto-resistance effect elements disposed at an interval of i.lambda. and the other of which includes two magneto-resistance effect elements disposed at an interval of (i+j).lambda., where i represents zero or an integer and 0&lt;j&lt;1). In this magnetic sensor, an output waveform obtained through add and subtract operations between outputs of the above pairs has a large gradient in the vicinity of the comparing level.
For example, as shown in FIG. 8, N and S magnetic poles are alternately disposed on a magnetic recording medium 21 at an interval of .lambda., and a pair of magneto-resistance effect elements 22 and 23 which are disposed spacedly at an interval of 0.2.lambda. in such a manner as to confront the magnetic recording medium, are connected to each other in series. Both ends of the elements are supplied with a voltage from a power source, and an output having a waveform as indicated by a character A of FIG. 9 is obtained at a connection point A of the magneto-resistance effect elements.
Likewise, a second pair of magneto-resistance effect elements 25 and 26 which are disposed spacedly at an interval of 0.8.lambda. in such a manner as to confront the magnetic recording medium, are connected to each other in series, and both ends of the connected elements are supplied with a voltage from the power source, to thereby obtain an output waveform as indicated by a character B of FIG. 9 at a conjunctive point B. In this case, in order to provide both outputs of the magneto-resistance effect elements with a suitable relative phase-difference, both pairs are positionally deviated from each other by 0.7.lambda.. A final output having a waveform as shown in FIG. 10 is obtained by adding both of the outputs A and B of the pairs.
The magnetic sensor thus constructed is superior in that the output of the magnetic sensor has a larger or sharper waveform in the vicinity of the comparing level, in comparison with a conventional magnetic sensor in which two pairs of magneto-resistance effect elements, one pair comprising two magneto-resistance, effect elements disposed at the interval of .lambda., are spacedly disposed at an interval of (N+1/2).lambda.. However, in the magnetic sensor using two pairs of magneto-resistance effect elements as described above, an alternating arrangement is required for current terminals, for example, in such a manner that Vcc, GND, Vcc and GND are alternately disposed as shown in FIG. 8. The current terminals are not integrally or commonly formed on substrate, so that a wire pattern in which four current terminals are individually electrically drawn out of the respective magneto-resistance effect elements is required and thus there is a probability that each element would be required to be large in size. Further, there frequently occur unfavorable results in manufacturing process and practical use because connection is required for the magneto-resistance effect elements. Still further, since the magnetic sensor adopting the above manner does not function as a magnetic sensor unless an adder for adding the outputs 1 and 2 of the two pairs of magneto-resistance effect elements is included in the device, high cost and complicated construction are required to apply the above magnetic sensor to a field in which plural magnetic sensors must be used.